I. Field of the Invention
This invention relates generally to apparatus for repairing and refurbishing the bearing surfaces of rotating shafts of large machines at a job site, and more particularly to a portable journal turning lathe that can easily be transported to a location in the field where a machine is to be repaired, mounted in place on the machine's shaft to be turned and then operated to remove any scoring and other surface irregularities from the shaft so that it is ready for replacement of its bearings.
II. Background of the Invention
In my earlier U.S. Pat. No. 6,065,378 I describe a portable journal turning lathe including a pair of clamping rings that are adapted to be centered at spaced-apart locations along a length of a shaft to be refurbished. Extending between the clamping rings is a plurality of guide shafts which slidingly support a split-ring clamshell assembly. A cutting tool carrier is affixed to the rotatable ring portion of the clamshell assembly such that when the movable ring is driven, the tool carrier orbits the shaft being refurbished. A single feed screw driven by a servomotor translates the clamshell assembly along the guide shaft.
In the earlier arrangement described in my '378 patent, only a single feed screw was used to move the clamshell assembly along the guide shafts. As such, the lathe described in my '378 patent had some tolerance problems when doing large shafts. When the cutting tool would dig into the shaft to be machined it would create resistance on the longitudinal movement of the clamshell assembly on the guide shafts. The side opposite the feed screw lags behind so that the cut of the cutting assembly was not square and concentric to the shaft being machined.
The journal turning lathe of the present invention obviates this drawback. Rather than having a single feed screw, my present invention employs two feed screws which are positioned and simultaneously driven so as to hold the clamshell carrying the cutting tool square and concentric to the cylindrical workpiece being machined. In the case of the present invention compared to my earlier arrangement, the workpiece is more effectively machined.